Distribution pattern of zoanthids (Cnidaria: Zoantharia) on a tropical reef

Abstract

Coastal reef environments support a great diversity of benthic species, which are physically arrayed according to their adaptations to biotic factors such as competition and to abiotic factors such as salinity and desiccation. Few studies have described adaptive strategies on rocky shores in tropical regions. This contribution deals with the spatial distribution of three species of zoanthids (Palythoa caribaeorum, Protopalythoa variabilis and Zoanthus sociatus) on flat sandstone reefs in north-eastern Brazil. Zoanthid distribution and abundances were determined as the percentage of cover along six transects, where 50 × 50 cm quadrats were sampled. Biotic data (influence of macroalgal cover) and abiotic data (relief, substrate type, temperature and salinity) were also taken along the transects to attempt to explain the zoanthid distribution. These species tended to colonize the middle and low intertidal zones, which are least exposed to air. Zoanthus sociatus apparently resists desiccation better than P. caribaeorum. Protopalythoa variabilis showed the highest abundance and frequency, occurring in the entire middle intertidal zone and colonized areas with high proportions of unconsolidated sediment. Desiccation was the main factor limiting the spatial distributions of the three species, although substrate composition and probably interspecific competition with macroalgae were also important. The results suggest that the zoanthids use a variety of these adaptive strategies, which account for their success on consolidated substrates. Continuous monitoring of changes in distribution patterns can be useful for indicating human impacts on marine biodiversity, providing insights for monitoring and conservation programmes.